Process for preparing cycloolefin random copolymer pellets

Abstract: Disclosed is a process for preparing cycloolefin random copolymer pellets, comprising adding an organic polar solvent to a solution of a copolymer obtained by copolymerizing ethylene and a specific cycloolefin and if desired an α-olefin other than ethylene, in an amount exceeding such an amount that the liquid mixture exhibits the cloud point, separating the copolymer solution utilizing phase separation phenomenon into a concentrated phase containing the cycloolefin random copolymer in a high concentration and a dilute phase containing said copolymer in a low concentration, feeding the obtained concentrated phase to an extruder where the solvents are removed and the copolymer is melted during extrusion processing, followed by pelletizing the copolymer. According to the invention, the steps for preparing cycloolefin random copolymer pellets can be reduced, and moreover, mold staining can be inhibited in the molding process of the resultant pellets because the pellets have low contents of the low molecular weight copolymer, the unreacted monomer, etc.

Description: The present invention relates to a process for preparing cycloolefin random copolymer pellets in a reduced number of steps and with prevention of mold staining when a molded product is formed from the pellets. The present inventors have proposed a variety of cycloolefin random copolymers formed from ethylene and specific cycloolefins, as described in, for example, Japanese Patent Laid-Open Publications No 168708/1985 and Japanese Patent Applications No. 220550/1984, No. 236828/1984, No. 236829/1984 and No. 242336/1984. The cycloolefin random copolymers described in these publications and applications have high transparency and excellent properties such as heat resistance, thermal aging resistance, chemical resistance, solvent resistance, dielectric properties and mechanical properties. Further, such cycloolefin random copolymers have good adhesion to substrates of various materials, even though they are a kind of polyolefin. Accordingly, the cycloolefin random copolymer can be used, for example, in the field of optical materials such as optical memory discs and optical fibers, and in the field of transparent container materials and packaging materials such as transparent films and transparent containers. The cycloolefin random copolymer is conventionally used in the form of pellets for the production of molded articles. In the conventional process for preparing the pellets, as shown in Fig. 2, a large number of steps are required prior to pelletizing the cycloolefin random copolymer, such as the steps of polymerization, deashing, filtration, precipitation-filtration, extraction-filtration, drying, and addition of stabilizer. After these steps, the cycloolefin random copolymer is fed to an extruder, melted in the extruder, and pelletized. That is, the cycloolefin random copolymer is generally prepared by copolymerizing ethylene and a cycloolefin in a hydrocarbon solvent in the presence of a catalyst, so that steps for removing the catalyst and the solvent are required prior to the pelletizing step. Further, the unreacted cycloolefin and a low molecular weight cycloolefin random copolymer, for example, which might cause mold staining in the molding process of the resultant pellets, still remain in the hydrocarbon solvent, so that they also must be removed prior to the pelletizing step. For preparing the cycloolefin random copolymer pellets, therefore, the catalyst, the reaction solvent, the unreacted cycloolefin and the low molecular weight cycloolefin random copolymer are removed through the many above-mentioned steps. The cycloolefin random copolymer must go through a large number of steps prior to the pelletizing step as described above, and hence the cost for preparing the pellets becomes relatively high. Moreover, the present inventors have found that the optical properties of the cycloolefin random copolymer, such as transparency, tends to lower every time the copolymer goes through each step after the polymerization step, though the lowering level is very low. EP-A-447 072 discloses a cycloolefin random copolymer containing substantially no polyethylene. The polyethylene formed as a side reaction product is separated and removed from the cycloolefin random copolymer solution. The present invention seeks to provide a process for preparing cycloolefin random copolymer pellets in which the number of steps for preparing the pellets can be reduced, mold staining hardly takes place when the pellets are molded into a product, and the inherent properties of the copolymer such as the optical properties are not marred. The present invention provides a process for preparing cycloolefin random copolymer pellets, comprising the steps of: adding to a copolymer solution of cycloolefin random copolymer [A] in hydrocarbon solvent, an organic polar solvent in an amount exceeding that at which the copolymer solution exhibits a cloud point and to give a liquid mixture; separating the liquid mixture into a lower phase containing cycloolefin random copolymer [A] in a higher concentration and an upper phase containing the copolymer [A] in a lower concentration; feeding the lower phase to an extruder where the solvents are removed and the cycloolefin random copolymer is melted during extrusion processing; and pelletizing the cycloolefin random copolymer; wherein the cycloolefin random copolymer [A] is obtainable by copolymerizing, in the presence of a catalyst, ethylene, optionally at least one other α-olefin, and at least one cycloolefin of formula (I) or (II): wherein n is 0 or 1; m is 0 or a positive integer; q is 0 or 1; each of R 1 to R 18 , R a and R b is the same or different and is hydrogen, halogen or a hydrocarbon group, wherein one or more of R 15 to R 18 may be linked together to form a monocyclic or polycyclic group optionally containing one or more double bonds or R 15 and R 16 , or R 17 and R 18 may together form an alkylidene group; wherein each of p and q is the same or different and is 0 or an integer of 1 or more; each of m and n is the same or different and is 0, 1 or 2; each of R 1 to R 19 is the same or different and is hydrogen, halogen or a hydrocarbon or alkoxy group; the carbon atom to which R 9 and R 10 are linked may be bonded directly or by way of an alkylene group of 1 - 3 carbon atoms to the carbon atom to which R 13 is linked or the carbon atom to which R 11 is linked; and R 15 and R 12 , or R 15 and R 19 may be linked together to form a monocyclic or polycyclic aromatic ring when each of n and m is 0. The copolymer solution may comprise: a solution containing a cycloolefin random copolymer [B] obtainable by copolymerizing ethylene and at least one cycloolefin of formula (I) or (II) and which has an intrinsic viscosity [η], as measured in decahydronaphthalene at 135 °C, of from 0.05 to 10 dl/g and a softening temperature (TMA) of at least 70 °C; and a solution containing a cycloolefin random copolymer [C] obtainable by copolymerizing ethylene, at least one other α-olefin and at least one cycloolefin of formula (I) or (II) and which has an intrinsic viscosity [η], as measured in decahydronaphthalene at 135 °C, of from 0.01 to 10 dl/g and a softening temperature (TMA) of lower than 70 °C; the amount of said solution of the copolymer [C] being from 1 to 100 parts by weight based on 100 parts by weight of said solution of copolymer [B]. In this process the liquid mixture is separated into a lower phase containing the cycloolefin random copolymers [B] and [C] in higher concentrations and an upper phase containing the copolymers [B] and [C] in lower concentrations. The cycloolefin random copolymer [C] may be a copolymer [D] obtainable by copolymerizing ethylene, propylene or 1-butene and at least one cycloolefin of formula (I) or (II). According to the present invention, the organic polar solvent is added to the cycloolefin random copolymer solution to form a phase-separated state whereby the unreacted cycloolefin and the low molecular weight cycloolefin random copolymer are transferred into the low-concentration (dilute) phase (i.e., the upper phase), the high-concentration (concentrated) phase (i.e., the lower phase) containing the cycloolefin random copolymer in a high concentration is separated out, and the concentrated lower phase separated is fed to an extruder where the solvents (the hydrocarbon solvent and the organic polar solvent) are removed and the cycloolefin random copolymer is melted during extrusion processing, and the copolymer is pelletized. Thus, the steps for preparing the pellets can be prominently reduced and simplified as compared with the conventional pelletizing process as shown in Fig. 2. Further, the low molecular weight cycloolefin random copolymer and the unreacted cycloolefin, which cause mold staining, can be removed in larger amounts than those in the conventional process by transferring them into the dilute upper phase. As a result, mold staining hardly takes place in the molding process of the resultant pellets. Furthermore, in the process for preparing pellets according to the present invention, the cycloolefin random copolymer is in the form of a liquid mixture, not in the form of solid as in the conventional process, and is fed to the extruder, so that shear stress applied to the copolymer can be markedly reduced, such that a crosslinked gel structure of the copolymer (e.g. cyclohexane-insoluble fine particles having a diameter of not less than 1 µm) is hardly produced, and the excellent properties inherent to the cycloolefin random copolymer are hardly marred. Fig. 1 shows an example of the process for preparing copolymer pellets according to the present invention. Fig. 2 shows an example of the conventional process for preparing copolymer pellets. The process for preparing cycloolefin random copolymer pellets according to the present invention will now be described in more detail. In the process for preparing cycloolefin random copolymer pellets according to the invention, a cycloolefin random copolymer is first prepared. The cycloolefin random copolymer prepared in this step includes a copolymer [A] of cycloolefins of formula (I) or (II) and ethylene; a copolymer [B] of the above cycloolefins and ethylene, said copolymer [B] having an intrinsic viscosity [η] of 0.05 to 10 dl/g and a softening temperature (TMA) of not lower than 70 °C; a copolymer [C] of the above cycloolefins, ethylene and at least one other α-olefin, said copolymer [C] having an intrinsic viscosity [η] of 0.01 to 10 dl/g and a softening temperature (TMA) of lower than 70 °C; and a copolymer [D] of the above cycloolefin, ethylene and propylene or 1-butene, said copolymer [D] having an intrinsic viscosity [η] of 0.01 to 10 dl/g and a softening temperature (TMA) of not lower than 70 °C. In formula (I), when q is 1 the ring using q is a 6-membered ring, and when q is 0 this ring is a 5-membered ring. In formula (I), R 1 to R 18 , R a and R b are each independently hydrogen, a halogen or a hydrocarbon. Examples of the halogen include fluorine, chlorine, bromine and iodine. Examples of the hydrocarbon include alkyl of 1 to 20 carbon atoms, cycloalkyl of 3 to 15 carbon atoms and an aromatic hydrocarbon group. Examples of alkyl include methyl, ethyl, propyl, isopropyl, amyl, hexyl, octyl, decyl, dodecyl, and octadecyl. These alkyl groups may be substituted with halogen atoms. An example of cycloalkyl is a cyclohexyl. Examples of the aromatic hydrocarbon group include phenyl and naphthyl. In formula (I), R 15 and R 16 , R 17 and R 18 , R 15 and R 17 , R 16 and R 18 , R 15 and R 18 , or R 16 and R 17 may be linked together (or cooperate with each other) to form a monocyclic or polycyclic group, and the thus formed monocyclic or polycyclic group may have a double bond. Examples of the monocyclic or polycyclic group are: In these cyclic groups, the carbon atoms numbered 1 and 2 are those to which the substituents R 15 (R 16 ) or R 18 (R 19 ) are linked. In formula (I), R 15 and R 16 , or R 17 and R 18 may together form an alkylidene group. This alkylidene group generally has 2 to 20 carbon atoms. Examples of the alkylidene group include ethylidene, propylidene and isopropylidene. In formula (II), R 1 to R 19 are each independently hydrogen, a halogen, a hydrocarbon group or alkoxy. In formula (II), the halogen has the same meaning as that in the formula (I). The hydrocarbon groups include generally alkyl of 1 to 20 carbon atoms and cycloalkyl of 3 to 15 carbon atoms or aromatic hydrocarbon groups. Examples of alkyl include methyl, ethyl, propyl, isopropyl, amyl, hexyl, octyl, decyl, dodecyl and octadecyl. These alkyl groups may be substituted by halogen atoms. Cycloalkyl includes, for example, a cyclohexyl group. The aromatic hydrocarbon groups include, for example, aryl and aralkyl. Examples include phenyl, tolyl, naphthyl, benzyl and phenylethyl. Examples of alkoxy include methoxy, ethoxy and propoxy. The carbon atom to which R 9 and R 10 are linked may be bonded directly or by way of an alkylene group of 1 to 3 carbon atoms to the carbon atom to which R 13 is linked or the carbon atom to which R 11 is linked. In the latter case, R 9 and R 13 , or R 10 and R 11 together form an alkylene group such as methylene (-CH 2 -), ethylene (-CH 2 CH 2 -) or propylene (-CH 2 CH 2 CH 2 -). Furthermore, in the case of n = m = 0, R 15 and R 12 , or R 15 and R 19 may be linked together to form a monocyclic or polycyclic aromatic ring. Examples of the aromatic ring which is formed with R 15 and R 12 in the case of n = m = 0 include: wherein q is as defined in formula (II). Cycloolefins of formula (I) or (II) include: bicyclo-2-heptene derivatives (bicyclohept-2-ene derivatives), tricyclo-3-decene derivatives, tricyclo-3-undecene derivatives, tetracyclo-3-dodecene derivatives, pentacyclo-4-pentadecene derivatives, pentacyclopentadecadienene derivatives, pentacyclo-3-pentadencene derivatives, pentaccylo-3-hexadecene derivatives, pentacyclo-4-hexadecene derivatives, pentacyclo-4-heptadecene derivatives, heptacyclo-5-eicocene derivatives, heptacyclo-4-eicocene derivatives, heptacyclo-5-heneicocene derivatives, octacyclo-5-dococene derivatives, nonacyclo-5-pentacosene derivatives, nonacyclo-6-hexacosene derivatives, cyclopentadiene-acenaphthylene adducts, 1,4-methano-1,4,4a,9a-tetrahydrofluorene derivatives and 1,4-methano-1,4,4a,5,10,10a-hexahydroanthoracene derivatives. Examples of the cycloolefins of formula (I) or (II) are: The bicyclo[2.2.1]hept-2-ene derivatives such as the tricyclo[4.3.0.1 2,5 ]-3-decene derivatives such as the tricyclo[4.4.0.1 2,5 ]-3-undecene derivatives such as the tetracyclo[4.4.0.1 2,5 .1 7,10 ]-3-dodecene derivatives such as the pentacyclo[6.5.1.1 3,6 .0 2,7 .0 9,13 ]-4-pentadecene derivatives such as the pentacyclo[7.4.0.1 2, 5.1 9,12 .0 8,13 ]-3-pentadecene derivatives such as the pentacyclopentadecadiene compounds such as the pentacyclo[8.4.0.1 2,5 .1 9,12 .0 8,13 ]-3-hexadecene derivatives such as the pentacyclo[6.6.1.1 3,6 .0 2,7 .0 9,14 ]-4-hexadecene derivatives such as the hexacyclo[6.6.1.1 3,6 .1 10,13 .0 2,7 .0 9,14 ]-4-heptadecene derivatives such as the heptacyclo-5-eicosene derivatives such as the heptacyclo[8.7.0.1 3,6 .1 10,17 .1 12,15 .0 2,7 .0 11,16 ]-4-eicosebe derivatives such as the heptacyclo [8.8.0.1 4,7 .1 11,18 .1 13,16 .0 3,8 .0 12,17 ]-5-heneicosene derivatives such as the octacyclo[8.8.0.1 2,9 .1 4,7 .1 11,18 .1 13,16 .0 3,8 ,0 12,17 ]-5-docosene derivatives such as the nonacyclo[10.9.1.1 4,7 .1 13,20 . 1 15,18 .0 2,10 .0 3,8 .0 12,21 .0 14,19 ]-5-pentacosene derivatives such as the nonacyclo [10,10,1.1 5,8 .1 14,21 .1 16,19 .0 2,11 .0 4,9 . 0 13,22 .0 15,20 ]-6-hexacosene derivatives such as and furthermore, The cycloolefin random copolymer can be prepared by, for example, polymerizing ethylene and the cycloolefin (I) or (II) and, if necessary, another α-olefin such as propylene or 1-butene, in a hydrocarbon medium (solvent) or the cycloolefin in the presence of a catalyst (a) formed from a hydrocarbon-soluble vanadium compound and a halogen-containing organoaluminium compound or a catalyst (b) formed from a compound of the Group IV transition metal containing a ligand having a pentadienyl skeleton or a lanthanoid compound and an organoaluminium oxy-compound, and if necessary, an organoaluminium compound. More specifically, for example, in a continuous polymerization apparatus, ethylene is copolymerized with tetracyclo[4.4.0.1 2,5 .1 7,10 ]-3-dodecene -dodecene (hereinafter sometimes abbreviated to "TCD-3") as the cycloolefin in a cyclohexane medium using VO(OCH 2 CH 3 )Cl 2 /Al(CH 2 CH 3 ) 1.5 Cl 1.5 as a catalyst under the conditions of a reaction temperature of 10 °C and a reaction time (residence time for the polymerization reaction) of 30 minutes, to prepare an ethylene/TCD-3 random copolymer. The hydrocarbon solvent employable herein is, for example, a non-polar solvent having 5 to 12 carbon atoms, such as cyclohexane. Also employable as the reaction medium is a compound which is used as a starting material and which is liquid at an operating temperature, such as a cycloolefin. Such a compound can be used singly or in combination with the above-mentioned non-polar solvent. The cycloolefin random copolymer, which is a copolymer of the above-described cycloolefin and ethylene, contains recurring units derived from ethylene and recurring units derived from the cycloolefin as its essential constituent units. In addition, the copolymer may contain recurring units derived from other monomers copolymerizable with ethylene and the above-mentioned cycloolefin, with the proviso that the properties of the target copolymer are ensured. The other monomers include olefins other than ethylene and the above-mentioned cycloolefins. Examples are: α-olefins of 3 to 20 carbon atoms such as propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethy-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicocene; cycloolefins such as cyclobutene, cyclopentene, cyclohexene, 3,4-dimethylcyclopentene, 3-methylcyclohexene. 2-(2-methylbutyl)-1-cyclohexene, cyclooctene, 3a,5,6,7a-tetrahydro-4 and 7-methano-1H-indene; norbornenes such as 2-norbornene, 5-methyl-2-norbornene, 5-ethyl-2-norbornene, 5-isopropyl-2-norbornene, 5-n-butyl-2-norbornene, 5-isobutyl-2-norbornene, 5,6-dimethyl-2-norbornene, 5-chloro-2-norbornene and 5-fluoro-2-norbornene; and non-conjugated dienes such as 1,4-hexadiene, 4-methyl-5-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 1,7-octadiene, dicyclopentadiene, 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene. These monomers can be used singly or in combination of two or more. In the cycloolefin random copolymer, the recurring units derived from monomers such as described above are usually contained in an amount of not more than 20 % by mol, preferably not more than 10 % by mol. A variety of polymerization processes for preparing cycloolefin random copolymers and catalysts used therefor are already known, and the above-mentioned copolymer can be prepared under the appropriately selected conditions in accordance with the processes proposed by the present applicant as described in, for example, Japanese Patent Laid-Open Publications No. 168708/1985, No. 120816/1986, No. 115912/1986 and No. 115916/1986, Japanese Patent Applications No. 95905/1986 and No. 95906/1986, and Japanese Patent Laid-Open Publications No. 271308/1986 and No. 272216/1986. In such cycloolefin random copolymers, the cycloolefin of formula (I) or (II) is considered to form recurring units of the following formula (III) or (IV): wherein m, n, q, R 1 -R 18 , R a and R b are each as defined in formula (I); or wherein m, n, p, q and R 1 -R 19 are each as defined in formula (II). In the cycloolefin random copolymer mentioned above recurring units derived from ethylene generally exist in the range of 40 to 90 mol%, preferably 50 to 85 mol%, and recurring units derived from the cycloolefin generally exist in the range of 10 to 60 mol%, preferably 15 to 50 mol%. The recurring units derived from ethylene and those derived from the cycloolefins are arranged at random and the copolymer is substantially linear. A substantially linear structure of the cycloolefin random copolymer is confirmed by the fact that the copolymer dissolves completely in decahydronaphthalene at 135°C. In addition, the compositions of ethylene and the cycloolefin can be measured by 13 C-NMR. In such cycloolefin random copolymers, the intrinsic viscosity [η] of the cycloolefin random copolymer [A] is generally 0.01 to 5 dl/g, preferably 0.1 to 3 dl/g, as measured in decahydronaphthalene at 135°C. The softening temperature (TMA), as measured by a thermomechanical analyzer, is generally 70°C or higher, preferably 70 to 250°C, more preferably 80 to 200°C, still more preferably 90 to 180°C. The glass transition temperature (Tg) of the cycloolefin random copolymer [A] is generally 50 to 230°C, preferably 60 to 180°C. The crystallinity, as measured by X-ray diffractometry, is generally 0 to 10%, preferably 0 to 7%, especially preferably 0 to 5%. In the process for preparing pellets according to the invention, the cycloolefin random copolymer solution containing the cycloolefin random copolymer [A] may be supplied to a deashing stage if desired, and then supplied to a phase separation stage. The cycloolefin random copolymer [B] can be prepared by copolymerizing ethylene and the cycloolefin of formula (I) or (II) in the same hydrocarbon solvent in the presence of the same catalyst as described before, usually at a temperature of -50 to 200 °C under a pressure of 0 to 4.9 MPa (0 to 50 kg/cm 2 -G). This polymerization can be conducted in, for example, a loop type reactor and a vessel type polymerization vessel equipped with a stirrer. In the cycloolefin random copolymer [B] thus obtained, the recurring units derived from ethylene usually exist in an amount of 40 to 85 % by mol, preferably 50 to 75 % by mol, and the recurring units derived from the cycloolefin usually exist in an amount of 15 to 60 % by mol, preferably 25 to 50 % by mol. The recurring units derived from ethylene and the recurring units derived from the cycloolefin are arranged at random and substantially linearly. A substantially linear and free from crosslinked gel structure of the cyloolefin random copolymer [B] can be confirmed by the fact that this copolymer perfectly dissolves in decahydronaphthalene at 135 °C. The intrinsic viscosity [η] of the cycloolefin random copolymer [B], as measured in decahydronaphthalene at 135 °C, is 0.05 to 10 dl/g, preferably 0.08 to 5 dl/g. The softening temperature (TMA) of the cycloolefin random copolymer [B], as measured by a thermomechanical analyzer, is at least 70 °C, preferably 70 to 250 °C. The glass transition temperature (Tg) of the cycloolefin random copolymer [B] is usually 50 to 230 °C, preferably 70 to 210 °C. The crystallinity of the cycloolefin random copolymer [B] as measured by X-ray diffractometry, is usually 0 to 10 %, preferably 0 to 7 %, more preferably 0 to 5 %. The cycloolefin random copolymer [C] can be prepared by copolymerizing ethylene, the aforementioned cycloolefin and at least one α-olefin other than ethylene in the same hydrocarbon solvent in the presence of the same catalyst under the same conditions as described in the preparation of copolymer [B]. The α-olefin other than ethylene may have 3 to 20 carbon atoms; examples include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene. Further, the cycloolefin random copolymer [C] may contain recurring units derived from at least one further monomer which is copolymerizable with ethylene, the α-olefin other than ethylene and the cycloolefin of formula (I) or (II), provided that it does not deteriorate the properties of the target pellets. As these copolymerizable monomers, those exemplified for the cycloolefin random copolymer [A) can be used. In the cycloolefin random copolymer [C], the recurring units derived from ethylene usually exist in an amount of 40 to 99 % by mol, preferably 75 to 98 % by mol; the recurring units derived from the cycloolefin usually exist in an amount of 1 to 40 % by mol, preferably 1 to 15 % by mol; and the recurring units derived from at least one α-olefin other than ethylene usually exist in an amount of 1 to 45 % by mol, preferably 1 to 35 % by mol. The recurring units derived from ethylene, the recurring units derived from the cycloolefin and the recurring units derived from the other α-olefin are arranged at random and substantially linearly. A substantially linear and free from crosslinked gel structure of the cycloolefin random copolymer [C] can be confirmed by the fact that this copolymer perfectly dissolves in decahydronaphthalene at 135 °C. The intrinsic viscosity [η] of the cycloolefin random copolymer [C] as measured in decahydronaphthalene at 135 °C, is 0.01 to 10 dl/g, preferably 0.08 to 5 dl/g. The softening temperature (TMA) of the cycloolefin random copolymer [C], as measured by a thermomechanical analyzer, is lower than 70 °C, preferably -40 to 60 °C. It is desired that the softening temperature of the cycloolefin random copolymer [C] is lower than that of the cycloolefin random copolymer [B], usually by 30 to 250 °C, preferably by 50 to 250 °C. The glass transition temperature (Tg) of the cycloolefin random copolymer [C] is usually -60 to 40 °C, preferably -50 to 10 °C. It is desired that the glass transition temperature of the cycloolefin random copolymer [C] is lower than that of the cycloolefin random copolymer [B], usually by 30 to 250 °C, preferably 100 to 240 °C. The crystallinity of the cycloolefin random copolymer [C], as measured by X-ray diffractometry, is usually 0 to 10 %, preferably 0 to 7 %, more preferably 0 to 5 %. In the second process for preparing pellets according to the invention, a solution containing the cycloolefin random copolymer [B] is mixed with a solution containing the cycloolefin random copolymer [C] in such a manner that the amount of the cycloolefin random copolymer [C] is 1 to 100 parts by weight, preferably 5 to 80 parts by weight, more preferably 10 to 70 parts by weight, based on 100 parts by weight of the cycloolefin random copolymer [B]. If the amount of the cycloolefin random copolymer [C] is less than 1 part by weight, the molded product formed from the resultant pellets is apt to have a lower impact resistance even though it has good rigidity. On the other hand, if the amount exceeds 100 parts by weight, the molded product has poor rigidity though it is has good impact resistance. Thus, when the amount of the copolymer [C] is outside the above range, there is a tendency of a poor balance between the rigidity and the impact resistance. In the second process for preparing pellets according to the invention, the cycloolefin random copolymer solution containing the cycloolefin random copolymers [B] and [C] is supplied to a deashing stage if desired, and then supplied to a phase separation stage. In the third process for preparing pellets according to invention, the above-mentioned cycloolefin random copolymer [B] and the cycloolefin random copolymer [D] are employed. The cycloolefin random copolymer [D] can be prepared by copolymerizing ethylene, the aforementioned cycloolefin and propylene or 1-butene in the same hydrocarbon solvent in the presence of the same catalyst as described before in the first process for preparing pellets, usually at a temperature of -50 to 200 °C under a pressure of 0 to 4.9 MPa (0 to 50 kg/cm 2- G). This polymerization can be conducted in, for example, a loop type reactor and a vessel type polymerization reactor equipped with a stirrer. In the cycloolefin random copolymer [D], the recurring units derived from ethylene usually exist in an amount of 40 to 99 % by mol, preferably 75 to 98 % by mol, and the recurring units derived from the cycloolefin usually exist in an amount of 1 to 40 % by mol, preferably 1 to 15 % by mol. When propylene is used as an essential component, the recurring units derived from propylene usually exist in an amount of 1 to 45 % by mol, preferably 1 to 35 % by mol. When 1-butene is used as an essential component in place of propylene, the recurring units derived from 1-butene usually exist in an amount of 1 to 45 % by mol, preferably 1 to 35 % by mol. The recurring units derived from ethylene, the recurring units derived from the cycloolefin and the recurring units derived from propylene or 1-butene are arranged at random and substantially linearly. A substantially linear and free from crosslinked gel structure of the cycloolefin random copolymer [D] can be confirmed by the fact that this copolymer perfectly dissolves in decahydronaphthalene at 135 °C. The intrinsic viscosity [η] of the cycloolefin random copolymer [D] as measured in decahydronaphthalene at 135 °C is 0.01 to 10 dl/g, preferably 0.08 to 5 dl/g. The softening temperature (TMA) of the cycloolefin random copolymer [D], as measured by a thermomechanical analyzer, is lower than 70 °C, preferably -40 to 60 °C. It is desired that the softening temperature of the cycloolefin random copolymer [D] is lower than that of the cycloolefin random copolymer [B], usually by 30 to 250 °C, preferably by 50 to 250 °C. The glass transition temperature (Tg) of the cycloolefin random copolymer [D] is usually -60 to 40 °C, preferably -50 to 10 °C. It is desired that the glass transition temperature of the cycloolefin random copolymer [D] is lower than that of the cycloolefin random copolymer [B], usually by 30 to 250 °C, preferably by 100 to 240 °C. The crystallinity of the cycloolefin random copolymer [D] as measured by X-ray diffractometry is usually 0 to 10 %, preferably 0 to 7 %, more preferably 0 to 5 %. In the third process for preparing pellets according to the invention, a solution containing the cycloolefin random copolymer [B] is mixed with a solution containing the cycloolefin random copolymer [D] in such a manner that the amount of the cycloolefin random copolymer [D] is 1 to 100 parts by weight, preferably 5 to 80 parts by weight, more preferably 10 to 70 parts by weight, based on 100 parts by weight of the cycloolefin random copolymer [B]. If the amount of the cycloolefin random copolymer [D] is less than 1 part by weight, the molded product formed from the resultant pellets is apt to have a lower impact resistance even though it has good rigidity On the other hand, if the amount exceeds 100 parts by weight, the molded product has poor rigidity though it has good impact resistance. Thus, when the amount of the copolymer [D] is outside the above range, there is a tendency of a poor balance between the rigidity and the impact resistance. In the third process for preparing pellets according to the invention, the cycloolefin random copolymer solution containing the cycloolefin random copolymers [B] and [D] is supplied to a deashing stage if desired, and then supplied to a phase separation stage. The first to third processes of the invention can be conducted as described hereinafter. For example, the reaction solution (copolymer solution) containing the cycloolefin random copolymer obtained above is supplied to a phase separation stage, preferably through a deashing stage, as shown in Fig. 1. The deashing is to remove the catalyst remaining in the copolymer solution by precipitation. That is, after the polymerization reaction is conducted as described above, the copolymer solution in which the cycloolefin random copolymer is dissolved is generally taken out of the reactor and deashed. In this stage, hot water and a pH adjuster are usually added to the copolymer solution taken out of the reactor. The pH adjustor is, for example, an aqueous solution of sodium hydroxide having a concentration of approx. 1 to 40 % by weight. By the addition of hot water and the pH adjustor, the copolymerization reaction stops and the catalyst dissolved in the copolymer solution is precipitated. In the deashing stage, the precipitated catalyst is removed from the copolymer solution after cooling the copolymer solution. After the deashing stage, the solution containing the cycloolefin random copolymer is led to a separation zone, where the copolymer solution is subjected to phase separation. In the separation zone, an organic polar solvent is added to the solution containing the cycloolefin random copolymer. Examples of the organic polar solvent are: ketones, such as ecetone, methyl ethyl ketone, diethyl ketone and methyl isobutyl ketone; alcohols, such as methanol, ethanol, propanol, isopropanol, butanol, sec-butanol and tert-butanol; esters, such as methyl acetate, ethyl acetate and propyl acetate; ethers, such as ethyl ether and tetrahydrofuran; and halides of aliphatic, aromatic and alicyclic hydrocarbons, such as methyl chloride, ethyl chloride and chlorobenzene. These organic polar solvents may be used singly or in combination. Of the organic polar solvents, ketones are preferably used, and of the ketones, acetone is particularly preferred. The copolymer solution exhibits a cloud point when the amount of the organic polar solvent added to the copolymer solution reaches a certain amount. In the invention, the organic polar solvent is added to the copolymer solution in an amount which is more than the above-mentioned amount at which the copolymer solution exhibits the cloud point. Further, it is preferred that the organic polar solvent is added in an amount which is more than the above-described one and in such an amount that the cycloolefin random copolymer is not precipitated or solidified. The amount of the organic polar solvent to be added varies depending upon, for example, the nature of the copolymer (e.g., molecular weight, molecular weight distribution, composition, composition distribution), concentration of the copolymer in the solution, kind of the hydrocarbon solvent, temperature and kind of the organic polar solvent added. For example, when 20 parts by volume of acetone is added at room temperature to 100 parts by volume of a cyclohexane solution containing 5 % by weight of the cycloolefin random copolymer, the copolymer solution exhibits the cloud point. In the invention, it is desired that the organic polar solvent is usually added in an amount of 1 to 5 times, preferably 1.1 to 3 times, as much as the amount by which the copolymer solution exhibits the cloud point. In general, as the amount of the organic polar solvent increases, the copolymer concentration in the concentrated phase becomes higher, while the copolymer concentration in the dilute phase becomes lower. Further, with the increase of the amount of the organic polar solvent, the dilute phase tends to selectively take up the low molecular weight cycloolefin random copolymer. Moreover, as a difference in the density between the concentrated phase and the dilute phase becomes larger, the phase separation between the concentrated phase and the dilute phase can be more efficiently carried out, whereby post treatments of each phases can be readily made. The copolymer solution to which the organic polar solvent has been added in an amount as described above is phase-separated into the concentrated phase containing the cycloolefin random copolymer in a relatively high concentration (generally, lower phase) and a dilute phase containing the cycloolefin random copolymer in a low concentration (upper phase). After the addition of the organic polar solvent, the phase separation of the copolymer solution can be carried out by, for example, gravity sedimentation, e.g., by allowing the copolymer solution to stand, or by means of centrifugal separation. In the invention, the concentrated phase, which is in general the lower phase, is taken out from the phase-separated copolymer solution. The lower phase (concentrated phase) solution thus taken out is then preferably sent to a heating stage. The heating is carried out by, for example, a heat exchanger such as a multi-tube type heat exchanger or a double-tube type heat exchanger. The concentrated phase solution is usually heated to 50 to 380 °C, preferably 150 to 300 °C. By heating the solution to such a temperature, the solvents and the unreacted cycloolefin which remains in a small amount can be very easily removed in the subsequent step carried out in an extruder. After the heating, the concentrated phase solution is fed to an extruder. In the extruder, the solvent and the unreacted cycloolefin still remaining in the solution in a small amount are removed, and the cycloolefin random copolymer produced is melted and then pelletized. Examples of the extruder used in the invention include conventionally known extruders such as a single-screw extruder, a twin-screw one-way extruder, a twin-screw two-way extruder and a planetary screw extruder. The extruder used in the invention is provided with a means for removing the solvent and the unreacted cycloolefin, for example, a vent. In the invention, it is preferred to use a twin-screw extruder provided with a back vent and a vacuum vent. The vacuum pressure of the vacuum vent portion is usually adjusted to atmospheric pressure to 0.1 Torr, preferably 100 to 1 Torr, by means of the vacuum vent. The barrel temperature of the extruder is usually adjusted to 180 to 380 °C, preferably 210 to 350 °C. Relatively large amounts of the solvent and the unreacted cycloolefin are removed by the back vent, and owing to the vacuum vent, the solvent and cycloolefin still remaining in extremely small amounts can be almost completely removed. The cycloolefin random copolymer extruded under the above conditions is generally filtered through a polymer filter and then pelletized. It is preferred that the difference between the pressure on the front side of the polymer filter and the pressure on the back side is not excessively large. There is no specific limitation on the shape and the size of the copolymer pellets obtained as above. Pellets of any shape and any size can be formed. Moisture is usually attached to the copolymer pellets obtained, so that the pellets are generally dried to remove moisture. Then, the pellets can be classified so as to remove, for example, fine particles having a weight of not more than 1/10 as much as the weight of the target pellets, and fine foreign substances. In the cycloolefin random copolymer pellets thus obtained, the unreacted cycloolefin and low molecular weight cycloolefin random copolymer contents are very low, and hence mold staining hardly occurs when a molded product is formed from the pellets. According to the present invention, the cycloolefin random copolymer pellets can be prepared without going through a large number of steps, which are essential in the conventional process, such as a precipitation step, a step of filtering the precipitated copolymer, a step of dispersing again the filtered copolymer in a solvent, a step of extracting the unreacted substance from the dispersion, a step of filtering the dispersion, and a step of drying the filtered dispersion. Hence, the cost for preparing the pellets can be reduced. According to the invention, moreover, the cycloolefin random copolymer is fed to the extruder in the form of a liquid mixture, and thereby shear stress applied to the copolymer can be reduced as compared with the conventional process shown in Fig. 2. As a result, formation of by-products (e.g., cyclohexane-insoluble fine particles having a diameter of not less than 1 µm), which cause lowering of the transparency of a molded product prepared from the resultant pellets, can be inhibited, accompanied by the preparation of the cycloolefin random copolymer. The cycloolefin random copolymer pellets prepared by the process of the invention can be used, for example, in the field of optical materials such as in optical disc substrates and optical fibers and in the field of transparent container materials and packaging materials such as in transparent films and transparent containers. Moreover, since the formation of by-products is reduced, the process of the invention is very suitable for preparing molding materials for forming optical disc substrates almost free from reading errors caused by nonuniformity of the substrate and for forming highly transparent films. Cycloolefin random copolymer pellets prepared according to the present invention may contain various additives, for example, a heat stabilizer, weathering stabilizer, antistatic agent, anti-slip agent, antiblocking agent, antifogging agent, lubricant, pigment, dye, natural oil, synthetic oil and wax, provided that the object of the invention is not marred. Stabilizers include, for example, phenolic antioxidants such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate]methane, alkyl ester of β-(3,5-di-t-butyl-4-hydroxyphenyl)propionic acid and 2,2'-oxamidobis[ethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)]propionate; aliphatic acid metal salts such as zinc stearate, calcium stearate and calcium 12-hydroxystearate; and aliphatic acid esters of polyhydric alcohols such as glycerin monostearate, glycerin monolaurate, glycerin distearate, pentaerythritol monostearate, pentaerythritol distearate and pentaerythritol tristearate, and phosphorous-containing stablizers such as tris(2,4-di-t-butylphenyl)phosphite. These stabilizers may be used singly or in combination. One example of a combination is the co-use of tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, tris(2,4-di-t-butylphenyl)phosphite, zinc stearate and glycerin monostearate. In the present invention, particularly preferred is a combination of the phenolic antioxidant and the aliphatic acid ester of a polyhydric alcohol. The aliphatic acid ester of a polyhydric alcohol is preferably an aliphatic acid ester of a polyhydric alcohol in which a part of alcoholic hydroxy group of the polyhydric alcohol having 3 or more hydroxy group is esterified. The aliphatic acid esters of polyhydric alcohols include, for example, aliphatic acid esters of glycerin such as glycerin monostearate, glycerin monolaurate, glycerin monomyristate, glycerin monopalmitate, glycerin distearate and glycerin dilaurate; and aliphatic acid esters of pentaerythritol such as pentaerythritol monostearate, pentaerythritol monolaurate, pentaerythritol dilaurate, pentaerythritol distearate and pentaerythritol tristearate. The phenolic antioxidant is used in an amount of 0 to 10 parts by weight, preferably 0 to 5 parts by weight, more preferably 0 to 2 parts by weight, based on 100 parts by weight of the cycloolefin resin. The polyhydric alcohol is used in an amount of 0 to 10 parts by weight, preferably 0 to 5 parts by weight, based on 100 parts by weight of the cycloolefin resin. The stabilizers are desirably added before melting of the cycloolefin random copolymer. Further, in the present invention, the cycloolefin random copolymer pellets may include, provided that the object of the invention is not marred, fillers such as silica, diatomaceous earth, alumina, titanium oxide, magnesium oxide, pumice powder, pumice balloons, aluminium hydroxide, magnesium hydroxide, basic magnesium carbonate, dolomite, calcium sulfate, potassium titanate, barium sulfate, calcium sulfite, talc, clay, mica, asbestos, glass fibers, glass flakes, glass beads, calcium silicate, montmorillonite, bentonite, graphite, aluminium powder, molybdenum sulfide, boron fibers, silicon carbide fibers, polyethylene fibers, polypropylene fibers, polyester fibers and polyamide fibers. According to the process of the present invention, cycloolefin random copolymer pellets substantially not containing a low molecular weight cycloolefin random copolymer and an unreacted cycloolefin can be prepared through simple steps. Further, since the cycloolefin random copolymer pellets do not substantially contain a low molecular weight cycloolefin random copolymer and an unreacted cycloolefin, mold staining hardly takes place when a molded product is formed from the pellets. Moreover, in the process for preparing cycloolefin random copolymer pellets according to the invention, the copolymer in the form of a liquid mixture is fed to the extruder, and thereby formation of by-products (e.g., cyclohexane-insoluble fine particles having a diameter of not less than 1 µm) caused by application of a shear stress to the cycloolefin random copolymer occurs at a lower level as compared with the conventional process. Hence, a molded product formed from the pellets has excellent optical properties as well as other excellent properties such as heat resistance, thermal aging resistance, chemical resistance, solvent resistance, dielectric properties, rigidity and impact resistance. Accordingly, the cycloolefin random copolymer pellets prepared by the process of the invention can be widely used in various fields such as in the field of optical materials, specifically high quality optical materials, e.g., optical memory discs, and in the field of engineering plastics. The present invention will now be further described in the following Examples. Measurements of various physical properties and evaluation methods thereof in the invention are described below. Melt flow rate [MFR] The melt flow rate [MFR] was measured at a temperature of 260 °C under a load of 2,160 g. Intrinsic viscosity [η] The intrinsic viscosity [η] was measured in decahydronaphthalene at 135 °C using an Atlantic type viscometer. Copolymer composition (% by mol) The content (% by mol) of the cycloolefin component was determined by measuring the height of the peak of the absorption band (1,026 cm -1 ) based on the cycloolefin component by infrared spectrophotometry. The content of ethylene was determined as the remainder of the copolymer. Volatile material [VM] The amount (% by weight) of the volatile material [VM] remaining in the cycloolefin random copolymer pellets was determined by measuring the change in weight of the pellets under the conditions of a temperature of 190 °C, a vacuum pressure of 133 Pa (1 Torr) and a period of 1 hour. Content of unreacted cycloolefin The content of the unreacted cycloolefin was determined by dissolving the cycloolefin random copolymer pellets in cyclohexane and subjecting the resultant solution to gas chromatography. Softening temperature [TMA] The softening temperature [TMA] was determined by the heat distortion behavior of a sheet having a thickness of 1.0 mm formed from the cycloolefin random copolymer pellets using a Thermomechanical Analyzer produced by Du Pont. In detail, a quartz needle was put on the sheet, and the sheet was heated at a heating rate of 5 °C/min under a load of 50 g. The temperature at which the needle entered into the sheet by 0.1 mm was taken as the softening temperature [TMA]. Example 1 [Preparation of catalysts] VO(OC 2 H 5 )Cl 2 was diluted with cyclohexane to prepare a vanadium catalyst having a vanadium concentration of 6.7 mmol/liter-cyclohexane. Separately, ethylaluminium sesquichloride (Al(C 2 H 5 ) 1.5 Cl 1.5 ) was diluted with cyclohexane to prepare an organoaluminium catalyst having an aluminium concentration of 107 mmol/liter-cyclohexane. [Polymerization] In a stirred vessel type polymerization reactor (inner diameter: 700 mm, reaction volume: 300 liters), copolymerization of ethylene and tetracyclo[4,4,0,1 2,5 ,1 7,10 ]-3-dodecene -dodecene (cycloolefin, hereinafter sometimes referred to simply as "tetracyclododecene") was continuously carried out to prepare a cycloolefin random copolymer [B]. In this copolymerization, the vanadium catalyst prepared above was fed to the polymerization reactor in such an amount that the vanadium catalyst concentration in the cyclohexane, i.e., a polymerization solvent, in the polymerization reactor was 0.35 mmol/liter. Separately, the above-prepared vanadium catalyst was beforehand diluted with cyclohexane, i.e., a polymerization solvent, so that the vanadium catalyst concentration in the resultant dilute solution (before feeding to the polymerizer) was 1.8 times as much as the catalyst concentration in the polymerization reactor. This dilute solution was also fed to the polymerizer. Further, ethylaluminium sesquichloride, as an organoaluminium compound, was fed to the polymerization reactor in such an amount that a ratio (Al:V) of aluminum (Al) to vanadium (V) was 8.0:1. Under the conditions of a polymerization temperature of 10 °C and a polymerization pressure of 1.0 kg/cm 2 -G, the above-mentioned copolymerization was continuously carried out. In a loop type reactor (internal tube diameter: 4B, external tube diameter: 6B, length: 32 m, vertical type), ethylene, tetracyclododecene and propylene (as an α-olefin) were copolymerized under the same conditions as for the preparation of the above-mentioned cycloolefin random copolymer [B] except that the pressure was 4 kg/cm 2 -G, to prepare a cycloolefin random copolymer [C]. [Deashing] The solution of the cycloolefin random copolymer [B] and the solution of the cycloolefin random copolymer [C], both solutions having being drawn out from the reactors, were introduced into a pipe to subject them to premixing. To the resultant mixture were added hot water at 80 °C and a NaOH solution (as a pH adjustor) having a concentration of 25 % by weight, to terminate the copolymerization reaction and to remove the catalyst remaining in the copolymer solution (deashing procedure). Prior to sending the deashed mixed solution to a phase separation zone, the mixed solution was transferred into a stirring vessel having an effective volume of 1.0 m 3 and stirred for 1 hour. [Phase separation] The mixed copolymer solution (concentration: 5 % by weight) transferred into the stirring vessel was led to the separation zone. With stirring in a 0.2 kiloliter stirring vessel in the separation zone, to the the copolymer solution was added acetone in an amount of 20 % by volume per 100 % by volume of the copolymer solution. At that time, the copolymer solution started to turn cloudy, that is, the solution reached the cloud point. To the copolymer solution was further added acetone, when the amount of acetone reached 55 % by volume, the solution was continuously drawn out from the 0.2 kiloliter stirring vessel and transferred into a 2.7 kiloliter rest vessel. Immediately after the copolymer solution was transferred into the rest vessel, a concentrated polymer solution started to sediment. After a residence time of 30 minutes, a concentrated phase containing the cycloolefin random copolymers in a higher concentration and a dilute phase containing them in a lower concentration were continuously drawn out from the vessel. The copolymer concentration in the concentrated phase was measured, and it was 34 % by weight. Further, the copolymer concentration in the dilute phase was measured, and it was 0.13 % by weight. The amount of the copolymer contained in the dilute phase was 3.2 % by weight based on the amount of the copolymers contained in both the dilute and the concentrated phases. The average molecular weight of the copolymer contained in the dilute phase was not more than 1/10 as much as the average molecular weight of the whole copolymer used. [Pelletizing] The concentrated phase solution thus drawn out was fed to a double-tube type heater (external tube diameter: 2B, internal tube diameter: 3/4B, length: 21 m) in which water vapor at 2.5 MPa (25 kg/cm 2 -G) was used as a heating source at a feed rate of 30 kg/hr, and heated to 205 °C. The concentrated phase solution subjected to the heating described above was then kneaded by a twin-screw extruder provided with multiple vents. The kneading was carried out using the vented extruder (intermesh type twin-screw extruder, screw diameter: 30 mm, L/D: 30, two-way rotation, number of back vent: 1, number of vacuum vent: 2) at a barrel temperature of 260 °C under a vacuum pressure of the vacuum vent portion of 666 Pa (5 Torr). Through the kneading, most of the unreacted cycloolefin was exhausted from the back vent of the extruder together with the polymerization solvent. Further, the polymerization solvent (cyclohexane) and the unreacted cycloolefin still remaining in the copolymer could be removed mostly by the vacuum vents. The copolymer was melt-extruded, and then filtered through a leaf type polymer filter made of SUS metal nonwoven fabric (nominal diameter: 5 µm, produced by Nippon Seisen K.K.), which was provided at the tip of the extruder, to obtain pellets having a diameter of about 3 mm. [Drying and classification of pellets] The obtained copolymer pellets were dried to remove moisture attached to the pellets, and classified to remove, for example, pellet-worn fine particles which had a weight of not more than 1/10 as much as the weight of the pellet, pellets having small diameters, fragments of broken pellets, fine foreign substances attached to the pellets, by an air classification device. The molecular weight of the cycloolefin random copolymer forming the obtained pellets (i.e., molecular weight of the copolymer recovered from the concentrated phase), the amounts of the unreacted cycloolefin and the V:M remaining in the pellets, the amount of the low molecular weight copolymer removed from the reaction system and the molecular weight thereof, and the molecular weight of the copolymer produced in the whole reaction system are set forth in Table 1. Comparative Example 1 The copolymer solution prepared and deashed in Example 1 was fed to a 200-liter stirring vessel at a feed rate of 261 kg/hr, and with intensive stirring in the vessel at ordinary temperature, to the copolymer solution was added acetone in an amount of 4.5 times by volume as much as the amount of the copolymer solution to precipitate a powdery cycloolefin random copolymer, so as to form a slurry. The slurry was filtered through a filter, and wet cake attached to the filter filaments was separated by back washing with acetone. After extraction of the unreacted cycloolefin at 75 °C for 3 hours while keeping the slurry concentration at 20 g/liter-acetone, the slurry was cooled to 40 °C and centrifuged to remove the solvent, so as to obtain a wet cake. The wet cake was dried at 90 °C under atmospheric pressure for 1 hour by a Nara-type twin-paddle dryer, and then further dried at 90 °C under 1.33 kPa (10 Torr) for 3 hours by a Tamagawa-type vacuum paddle dryer. The dried product was pelletized by an extruder (intermesh type twin-screw extruder, screw diameter: 44 mm, L/D: 30, two-way rotation, number of atmospheric pressure vent: 1) at a barrel temperature of 260 °C. The molecular weight of the cycloolefin random copolymer forming the obtained pellets (i.e., molecular weight of the copolymer recovered from the slurry), the amount of the unreacted cycloolefin and the VM remaining in the pellets, the amount of the low molecular weight copolymer removed from the reaction system and the molecular weight thereof, and the molecular weight of the copolymer produced in the whole reaction system are set forth in Table 1. Comparative Example 2 The copolymer solution prepared and deashed in Example 1 was directly fed to a double-tube type heater (external tube diameter: 2B, internal tube diameter: 3/4B, length: 21 m) at a feed rate of 261 kg/hr without removing the low molecular weight polymer, for example, by means of the phase separation as in Example 1, and was heated to 180 °C Then, from the copolymer solution thus heated, the polymerization solvent and most of the unreacted cycloolefin were removed by the use of a double-tube type flash drier (external tube diameter: 2B, internal tube diameter: 3/4B, length: 27 m) and a flash hopper (volume: 200 liters). Water vapor at 2.5 MPa (25 kg/cm 2 ) was used as a heat source of the double-tube type flash dryer. The copolymer subjected to the above flash drying was then kneaded using a vented extruder (intermesh type twin-screw extruder, screw diameter: 30 mm, L/D: 32, two-way rotation, number of back vent: 1, number of vacuum vent: 2) at a barrel temperature of 260 °C and a vacuum pressure of each vacuum vent portion of 666 Pa (5 Torr). Pellets were prepared from the copolymer in the same manner as described in Example 1. The molecular weight of the cycloolefin random copolymer forming the obtained pellets (i.e., molecular weight of the copolymer recovered from the concentrated solution after heating), the amount of the unreacted cycloolefin and the VM remaining in the pellets, the amount of the low molecular weight copolymer removed from the reaction system and the molecular weight thereof, and the molecular weight of the copolymer produced in the whole reaction system are set forth in Table 1. Molecular weight of the copolymer prepared Molecular weihgt of the copolymer recovered Low molecular weight copolymer removed Unreacted cyclo-olefin in pellets (wt.%) VM in pellets (wt.%) Amount (wt%) Molecular weight Ex. 1 67,800 76,700 3.2 5,500 0.04 0.07 Comp. Ex. 1 67,800 70,000 0.3 1,500 0.02 0.10 Comp. Ex. 2 67,800 67,800 - - 0.04 0.07

Claims: A process for preparing cycloolefin random copolymer pellets, comprising the steps of: adding to a copolymer solution of cycloolefin random copolymer in hydrocarbon solvent, an organic polar solvent in an amount exceeding that at which the copolymer solution exhibits a cloud point and to give a liquid mixture; separating the liquid mixture into a lower phase containing cycloolefin random copolymer in a higher concentration and an upper phase containing the copolymer in a lower concentration; feeding the lower phase to an extruder where the solvents are removed and the cycloolefin random copolymer is melted during extrusion processing; and pelletizing the cycloolefin random copolymer; wherein the cycloolefin random copolymer is obtainable by copolymerizing, in the presence of a catalyst, ethylene, optionally at least one other α-olefin, and at least one cycloolefin of formula (I) or (II): wherein n is 0 or 1; m is 0 or a positive integer; q is 0 or 1; each of R 1 to R 18 , R a and R b is the same or different and is hydrogen, halogen or a hydrocarbon group, wherein one or more of R 15 to R 18 may be linked together to form a monocyclic or polycyclic group optionally containing one or more double bonds or R 15 and R 16 , or R 17 and R 18 may together form an alkylidene group; wherein each of p and q is the same or different and is 0 or an integer of 1 or more; each of m and n is the same or different and is 0, 1 or 2; each of R 1 to R 19 is the same or different and is hydrogen, halogen or a hydrocarbon or alkoxy group; the carbon atom to which R 9 and R 10 are linked may be bonded directly or by way of an alkylene group of 1 - 3 carbon atoms to the carbon atom to which R 13 is linked or the carbon atom to which R 11 is linked; and R 15 and R 12 , or R 15 and R 19 may be linked together to form a monocyclic or polycyclic aromatic ring when each of n and m is 0. A process according to claim 1 in which the copolymer solution comprises a cycloolefin random copolymer [A] obtainable by copolymerising ethylene and at least one cycloolefin of formula (I) or (II) and has an intrinsic viscosity [η], as measured in decahydronaphthalene at 135°C, from 0.01 to 5 dl/g and a softening temperature (TMA) of at least 70°C. A process according to claim 2 wherein the cycloolefin random copolymer [A] comprises 40 to 90% mol recurring units derived from ethylene and has a glass transition temperature [Tg] from 50 to 230°C and a crystallinity, measured by X-ray diffractometry, up to 10%. A process according to claim 1 wherein the copolymer solution comprises: a solution containing a cycloolefin random copolymer [B] obtainable by copolymerizing ethylene and at least one cycloolefin of formula (I) or (II) and which has an intrinsic viscosity [η], as measured in decahydronaphthalene at 135°C, of from 0.05 to 10 dl/g and a softening temperature (TMA) of at least 70°C; and a solution containing a cycloolefin random copolymer [C] obtainable by copolymerizing ethylene, at least one other α-olefin and at least one cycloolefin of formula (I) or (II) and which has an intrinsic viscosity [η], as measured in decahydronaphthalene at 135°C, of from 0.01 to 10 dl/g and a softening temperature (TMA) of lower than 70°C; the amount of said solution of copolymer [C] being from 1 to 100 parts by weight based on 100 parts by weight of said solution of copolymer [B]. A process according to claim 4 wherein: cycloolefin random copolymer [B] comprises 40 to 85% mol recurring units derived from ethylene and has a glass transition temperature [Tg] from 50 to 230°C and a crystallinity, measured by X-ray diffractometry, up to 10%; and cycloolefin random copolymer [C] comprises 40 to 99% mol recurring units derived from ethylene and has a glass transition temperature [Tg] from -60 to 40°C and a crystallinity, measured by X-ray diffractometry, up to 10%. A process according to claim 4 or 5 wherein the cycloolefin random copolymer [C] is a copolymer [D] obtainable by copolymerising ethylene, propylene or 1-butene and at least one cycloolefin of formula (I) or (II). A process according to any one of the preceding claims which further comprises deashing the copolymer solution prior to adding the organic polar solvent. A process according to any one of the preceding claims which further comprises adding a stabilizer prior to melting the random cycloolefin copolymer during extrusion processing.

Inventors: OKABE MASAYUKI, SUEYOSHI TOMOKO, WAKATSURU KENJI, OKABE, MASAYUKI, SUEYOSHI, TOMOKO, WAKATSURU, KENJI, OKABE, MASAYUKI, C/O MITSUI PETROCHEM. IND., LTD., SUEYOSHI, TOMOKO, C/O MITSUI PETROCHEM. IND., LTD., WAKATSURU, KENJI, C/O MITSUI PETROCHEM. IND., LTD.
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1994
Main classification: C08F210
IPC codes: C08F210, C08G61, B29B9, B29K23, C08J3